Microwave is broadly used as a heat source for electronic ranges and industrial heating furnaces. When compared with conventional devices for external heating of reaction targets, microwave is characterized by high efficiency and rapid heating of reaction targets since microwave is able to directly or indirectly heat polar dielectric substances not only heating water contained in substances.
It was recently found that microwave irradiation can promote chemical reactions of reaction targets and, as a consequence, use of microwave not only for heating devices but also for chemical reaction devices for rapid chemical reaction attracts attention of ones skilled in the art. For this reason, various experimental devices for use of microwave have been developed.
Microwave heating experimental devices are classified into three major groups, i.e. matching type waveguides connected at one end to matched loads, short circuit type waveguides with short circuit ends and cavity resonation type waveguides with cavity resonators. In general, chemical reactions are carried out with reaction targets being placed within these heating devices.
The matching type waveguide can be usually used without any adjustment. But the waveguide of this type has a disadvantage that only a part of the power generated by transmitted microwave can be utilized since action is performed only at the moment of passage of microwave through reaction targets due to their structural characteristics. Despite such disadvantage, the waveguide of this type now enjoys increasing use in the art because of its high ability for promotion of chemical reactions.
The short circuit type waveguides are able to utilize reflected microwave. The waveguide of this type has an advantage of improvement in operating efficiency through phase adjustment in which phases of advancing and reflected microwave are matched at the position of reaction targets. Nevertheless, it has a disadvantage that the short circuit position needs to be adjusted in accordance with difference and variation in dielectric characteristics of the reaction targets.
Square waveguides are generally used for the above-described both types of waveguides as disclosed in Japanese Patent Opening 2002-079078. The major disadvantage of these types of waveguides is insufficient operating efficiency caused by partial utilization of the power generated by microwave. As known, high operating efficiency is a very important requirement for reaction devices used in chemical plants.
The cavity resonation type waveguide has an advantage of extremely high operating efficiency thanks to repeated irradiation of microwave onto reaction targets via multiple reflections by the wall defining the cavity. Despite such advantage, the waveguide of this type has a disadvantage that tuning by adjustment of resonant frequencies is inevitable in accordance with difference and variation in characteristics of the reaction target.
One more important requirement for chemical reaction devices is uniformity in reaction. In order to suffice this requirement, it is necessary to irradiate microwave of at least in average and cumulatively uniform intensity on reaction targets. Presently, devices unsuited for uniform heating are used experimentally.
It is therefore highly required presently to develop microwave chemical reaction devices which can afford high efficiency characteristics of the cavity resonation type waveguides with easy adjustment of the matching type waveguides.